Campbell Andrew, Holstege Dirk, Swezey Robert, Medina-Cleghorn Daniel
Department of Environmental Toxicology, UC Davis, Davis, California, USA.
J Toxicol Environ Health A. 2008;71(19):1338-47. doi: 10.1080/15287390802240975.
Previous lab studies implicated the sulfoxidation pathway of molinate metabolism to induce testicular toxicity. Once molinate is metabolized to molinate sulfoxide, it undergoes further phase II metabolism either spontaneously, enzyme catalyzed, or both to form glutathione-conjugated molinate. This study compared the metabolic capability of rat and human liver cytosol to form a glutathione (GSH)-conjugated metabolite of molinate. The GSH conjugation of molinate sulfoxide in rat cytosol was described by the constants Km of 305 microM and Vmax of 4.21 nmol/min/mg cytosol whereas the human values were 91 microM and 0.32 nmol/min/mg protein for Km and Vmax, respectively. At the same 1 mM GSH concentration, the in vitro bimolecular nonenzymatic rate constant of 3.02 x 10(-6) microM(-1) min(-1) was calculated for GSH conjugation of molinate sulfoxide. Specific activity for rat and human glutathione transferase was calculated to equal 1.202 +/- 0.25 and 0.809 +/- 0.45 micromol/min/mg protein, respectively by 1-chloro-2,4-dinitrobenzene (CDNB) assay. Compared to a conventional GSH depletion model (BSO + DEM combination), molinate alone was nearly as effective in reducing GSH levels by approximately 90 and 25% in liver and testes, respectively. The impact of molinate sulfoxide's ability to adduct glutathione transferase and inhibit the production of the glutathione conjugated metabolite was examined and found to be negligible.
先前的实验室研究表明，禾草丹代谢的亚砜氧化途径会诱发睾丸毒性。一旦禾草丹代谢为禾草丹亚砜，它会自发地、酶催化地或两者兼而有之进行进一步的II相代谢，形成谷胱甘肽结合的禾草丹。本研究比较了大鼠和人肝细胞溶胶形成禾草丹谷胱甘肽（GSH）结合代谢物的代谢能力。大鼠肝细胞溶胶中禾草丹亚砜的GSH结合作用由常数Km为305微摩尔/升和Vmax为4.21纳摩尔/分钟/毫克细胞溶胶来描述，而人的Km和Vmax值分别为91微摩尔/升和0.32纳摩尔/分钟/毫克蛋白质。在相同的1毫摩尔/升GSH浓度下，计算出禾草丹亚砜GSH结合作用的体外双分子非酶速率常数为3.02×10^(-6)微摩尔^(-1)分钟^(-1)。通过1-氯-2,4-二硝基苯（CDNB）测定法，计算出大鼠和人谷胱甘肽转移酶的比活性分别为1.202±0.25和0.809±0.45微摩尔/分钟/毫克蛋白质。与传统的GSH耗竭模型（BSO+DEM组合）相比，单独使用禾草丹在降低肝脏和睾丸中GSH水平方面几乎同样有效，分别降低了约90%和25%。研究了禾草丹亚砜加合谷胱甘肽转移酶并抑制谷胱甘肽结合代谢物产生的能力的影响，发现其影响可忽略不计。
